Se eu tiver sorte, vou encontrar outra vaga de garagem.

Because Portuguese normally uses the future subjunctive after se when talking about a real possibility in the future.

So:

• Se eu tiver sorte = If I’m lucky / If I have luck
• not Se eu tenho sorte
• not Se eu terei sorte

This is a very common pattern:

• Se eu tiver tempo, vou. = If I have time, I’ll go.
• Se eles chegarem cedo, começamos. = If they arrive early, we’ll start.

English usually uses the present after if. Portuguese often uses the future subjunctive instead.

Tiver is the future subjunctive form of the verb ter (to have) for eu and ele/ela/você.

The future subjunctive of ter is:

• eu tiver
• você/ele/ela tiver
• nós tivermos
• vocês/eles/elas tiverem

So in this sentence, tiver comes from ter.

Because tenha is the present subjunctive, and that is not the normal form used after se for future conditions like this.

Compare:

• Se eu tiver sorte, vou encontrar... = If I’m lucky, I’ll find...
• Espero que eu tenha sorte. = I hope I’m lucky.

So:

• after se
  • future idea → usually future subjunctive
• after expressions like espero que, talvez, etc. → often present subjunctive

Both are correct, but vou encontrar is much more common in everyday Brazilian Portuguese.

• vou encontrar = I’m going to find / I will find
• encontrarei = I will find

In Brazil, ir + infinitive is very natural and common in speech:

• vou sair
• vamos ver
• ele vai chegar

Encontrarei sounds a bit more formal, literary, or emphatic.

Not always. Portuguese often drops subject pronouns because the verb ending already shows the person.

So both are possible:

• Se eu tiver sorte, vou encontrar outra vaga de garagem.
• Se tiver sorte, vou encontrar outra vaga de garagem.

Including eu can add clarity or emphasis, but it is not required.

Because ter sorte is a fixed, idiomatic expression meaning to be lucky or to have luck.

So Portuguese says:

• ter sorte
• ter azar

not usually:

• ter a sorte in this meaning

But ter a sorte de is a different structure:

• Tive a sorte de conhecer ela. = I had the good fortune to meet her.

In your sentence, tiver sorte is the normal idiomatic choice.

It means parking space or parking spot.

Even though vaga can also mean vacancy or opening in other contexts, in vaga de garagem it means a space for parking a car.

Examples:

• Comprei um apartamento com vaga de garagem. = I bought an apartment with a parking space.
• Não tem vaga de garagem aqui. = There’s no parking space here.

So here it does not mean a job vacancy.

Vaga de garagem is the standard expression for a parking space.

It works like a set noun phrase:

• vaga de garagem = parking space / garage parking spot

Vaga na garagem is possible, but it means more literally a spot in the garage and sounds less like the fixed everyday term.

A useful difference is:

• vaga de garagem = a parking space as a type of thing
• vaga na garagem = a space located in the garage

Because outra can already function as a determiner by itself, just like another in English.

So:

• outra vaga = another parking space

You can sometimes hear uma outra vaga, but it is less common here and can sound more emphatic or stylistically marked. In most everyday sentences, outra vaga is the natural choice.

Usually outra means another or a different one, depending on context.

In this sentence, it suggests that the speaker is looking for a different parking spot from the one they wanted or had before.

So outra vaga de garagem could mean:

• another available spot
• a different parking space

The exact nuance depends on the situation.

Because the sentence starts with a conditional clause:

• Se eu tiver sorte = If I’m lucky

When that clause comes first, Portuguese normally separates it from the main clause with a comma:

• Se eu tiver sorte, vou encontrar outra vaga de garagem.

If the order is reversed, the comma is often omitted:

• Vou encontrar outra vaga de garagem se eu tiver sorte.

Yes. That is the most natural English translation.

Literally, Portuguese says something like If I have luck, but English normally says If I’m lucky.

So this is a good example of an idiomatic difference:

• Portuguese: ter sorte
• English: be lucky

The meanings match, even though the wording is different.